The present invention relates to a nuclear reactor cooled by a liquid metal and more specifically relates to supporting the liquid metal-filled vessel and the contained reactor core.
It is known that for the purpose of providing biological protection the vessel of a fast neutron nuclear reactor is placed in a concrete vessel shaft and its upper part is sealed by a metal slab, whose gaps and openings are filled with concrete. In solutions used on the Rhapsodie, Phenix and Super Phenix reactors, the slab rests on an annular bearing surface formed in the upper part of the vessel shaft and the vessel is directly suspended on said slab. The vessel is filled with a primary liquid metal such as sodium, which cools the reactor core by transferring the heat given off in the reactor core to exchangers in which a secondary fluid circulates, which is generally also sodium. The circulation of the liquid metal in the core and in the exchangers is brought about by pumps. The primary sodium temperature is close to 540.degree. C. at the outlet from the core, i.e. in the upper part of the vessel, whilst it drops to about 400.degree. C. at the outlet from the exchangers, i.e. in the lower part of the vessel.
Hereinafter the term "hot" corresponds to the temperature of the liquid metal leaving the core, the term "tepid" to the temperaure of the liquid metal leaving the exchangers and reentering the core and the term "cold" to a temperature close to ambient temperature, but which may for example reach the fusion temperature of the liquid metal, i.e. approximately 100.degree. C. for sodium.
In the best known constructions the reactor vessel is suspended from the upper slab and transmits to it a considerable load. To prevent excessive creep of the upper part of the vessel walls, it is necessary to cool the same by circulating tepid sodium along the said walls. This leads to a certain thermodynamic loss and this arrangement also requires the use of baffles which are difficult to construct. In addition, suspended vessel are to a certain extent sensitive to possible seismic movements.
It has also been previously proposed to place the tepid vessel bottom on the bottom of the cold vessel shaft by means of distributed supports permitting radial differential expansion movements. These supports have, for example, been constituted by rollers or rods, or even Stellite or graphite blocks. This solution has not been adopted because it did not appear to offer sufficient reliability.
Another solution which has in fact been used consists of supporting the tepid bottom vessel in its lower peripheral part by radially displaceable supports. The supports then receive high individual stresses, but can be more easily inspected. However, compared with suspended vessels there is a need to radially transfer internal loads.